In a communications system, wireless communications links between transmitters and receivers are often affected by multiple factors. RF signals from the transmitters radiate in multiple directions and are reflected by different surfaces at multiple locations. Therefore, the receivers may simultaneously receive RF signals directly from the transmitters without reflections, as well as multiple reflected RF signals, which are referred to as multipath signals. Sometimes a receiver may be blocked from receiving an RF signal directly from a transmitter, wherein the receiver may receive only reflected signals. Such blocking is known as shading. Interfering RF signals may also be transmitted to the receiver directly, indirectly, or both. Movement of the transmitter, the receiver, or both may change these conditions. Interfering RF signals may come and go, and may originate from moving transmitters. As a result, conditions of the wireless communications links are often changing. Notably, changing the location of a transmitter antenna or a receiver antenna may temporarily improve or degrade a communications link.
Some systems may select one or more of multiple transmit antennas, multiple receive antennas, or both to provide spatial diversity in the communications system and improve overall performance. However, the effectiveness of antenna selection may be limited by the ability of the system to quickly measure and respond to changing RF link conditions. Thus, there is a need for a wireless communications system that can measure RF link conditions and select at least one antenna based on the RF link conditions rapidly enough to be effective.